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Day July 7, 2010

DDT may not be the longterm answer to the problem of malaria in Uganda.


Dear forum,

I have just completed studying  an advanced  module on malaria and I don’t think former MP for Lubaga South,Ken Lukyamuzi, should be crucified for refusing to use DDT. DDT may not be the longterm answer to the problem of malaria.

The focus of control should be directed towards the high risk groups (children under 5 years, pregnant women), prompt diagnosis and adequate treatment of malaria, intermittent presumptive treatment of pregnant women, prophylaxis for non-immune short-term visitors.

Another cheaper reliable method of control would be supplying of free long-term insecticide treated mosquito nets. Because the weather and environmental conditions are very favourable for the growth of malaria parasites and their mosquito vectors, DDT may not be able to eliminate malaria before significant resistance to it by mosquitoes has developed.

Prompt diagnosis and treatment will reduce the number of people carrying parasites, while bed nets will reduce the mosquito density.

The government has not also yet explained whether Ugandan mosquitoes are sensitive to DDT.The problem with the Ugandan government is corruption. When a drug company strikes a deal with a Ugandan policy maker, it goes on to sign a long term contract with the company without any research. For example, they signed a 25 year contract with a company that manufactures COARTEM (first line anti-malarial drug in Uganda) but this drug has started showing signs of resistance before even five years have elapsed.

From epidemiological and economic points of view, I don’t think DDT is the first priority to our malaria problem. Let the government first thoroughly explain the feasibility and safety of using DDT visa vie other modes of control because the harm DDT might cause to living organisms including humans in the long term may be worse than the likely short-term benefits.

What I want to say is that different malaria situations require different control measures and the situation in some parts of Uganda such as Apac, is best handled using a strategy cheaper and more feasible than spraying. In brief, I wanted to say the following:

  • It is impossible to eradicate mosquitoes using DDT, so this goal of control is unrealistic.
  • The benefits of and applicability of using DDT have not been investigated

Although Ken’s argument is about the environmental effect of DDT, my argument is about the feasibility and cost-effectiveness of this strategy. One needs to know the following facts:

  • The type of malaria transmitting mosquitoes (female anopheles gambiese) in Uganda only bite at night (from dusk on wards)
  • Both methods (nets and Indoor residual spraying-IRS) use the same principle of control, i.e reduce the number of mosquitoes by killing them on contact. Every mosquito that enters the house must not leave alive.
  • Mosquitoes adapt different feeding behaviours (either feed on humans or cattle, either bite outside or inside and after feeding they can either rest inside the house on the walls or outside)

Let’s now compare the two methods: The method of using spraying on the walls assumes that the mosquitoes bite indoors and rest indoors on the walls to digest their blood meal. Once mosquitoes realise the toxicity of the walls, they can adapt behaviour of resting outside the house or atleast a proportion of them (if this happens all the investment will be a flop!)

The use of DDT has the potential of selecting for mosquitoes that are resistant to DDT, in other words as the sensitive mosquitoes die, the proportion of resistant mosquitoes will increase and we shall go back to square zero after the heavy investment.

What determines its effectiveness? The type of walls of houses. Although it may be feasible in towns where houses are plastered and painted, it may not be the same in a rural mud house or even a hut. The biggest proportion of Ugandans live in houses where use of IRS is of limited effectiveness

Cost!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  • The amount of chemical necessary to spray a single two bed roomed house can treat hundreds of bed nets
  • Equipment for spraying (protective gear, sprayers), transport, number of personnel, allowances etc..

BED NETS

Bed nets work on the assumption that a mosquito is attracted to a person inside the net by some chemicals including carbon dioxide. It hits the net and is killed by the chemical on the net. The mosquito has little room for adaptation unlike IRS where a mosquito must rest on the wall after feeding for it to be killed and it can decide to rest outside if the inside is hostile.

Its effect not determined by the type of walls, even if someone is in a grass thatched hat.

Cost of the Chemical is minimal, no equipment, one person can supply and demonstrate use of a net in one central place (how many costs have you eliminated?)

In conclusion I am saying that in Uganda, IRS is not feasible and is not cost-effective given the many hindrances to its effectiveness. I think someone was promised something to push for a method that is not feasible and cost-effective. This is before we think of its long term effect to the environment. But note that my view is a purely scientific, not based on hatred of the corrupt NRM government!!!!

Abu-Baker Ggayi

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